Monday, May 21, 2012

In the winter of 1780, New York Harbor froze, allowing people to walk from Manhattan to Staten Island for the first time in recorded history. The deep freeze didn’t just occur in New York: For close to 500 years, beginning around the end of the Middle Ages and lasting into the early 19th century, unusually cold conditions blanketed much of the Northern Hemisphere.

Climate scientists now call this period of cooling the Little Ice Age. When exactly this period began, what triggered it and how it was sustained for so long are matters of much debate. But a new study, published in Geophysical Research Letters, may answer all three puzzles.

“Estimates regarding the onset of the Little Ice Age range from the 13th century to the 16th century,” says Gifford Miller, a climate scientist at the University of Colorado at Boulder and lead author of the new study. “More exact dates have been totally ambiguous and there is little consensus.”

To narrow the date of onset, Miller and colleagues radiocarbon dated dead vegetation emerging from ice caps on Baffin Island in the Canadian Arctic to determine when the plants died due to the initial encroachment of snow and ice. Most of the dates clustered at two periods of time: 1275 and 1450.

“Everybody tends to think of this as a gradual cooling, so we were quite surprised when we got the dates back,” Miller says. During both cold snaps, plants at lower elevations froze at approximately the same time as those at higher elevations, indicating a swift onset. Testing of sediment cores from glacial lakes in Iceland also indicated a change in erosion rates in the late 13th century and again in the 15th century.

Armed with more exact dates, Miller and colleagues pinpointed a likely culprit: a period of active volcanism, starting with an eruption in 1275 and continuing on and off through the early 1800s, with at least four major volcanic eruptions occurring during this time period.

Volcanism is often implicated in periods of abrupt cooling. After the 1991 eruption of Mount Pinatubo in the Philippines, for example, global temperatures dropped by half a degree Celsius due to airborne particulate matter blocking solar radiation. But the effects don’t usually last more than a few years, says David Schneider, a climate scientist at the National Center for Atmospheric Research in Boulder, Colo., who was not involved in the new study.

“Volcanism explains the abruptness but it can’t account for the longevity” of the Little Ice Age, Schneider says. “This has always been the problem with the volcanic explanation of the Little Ice Age. Volcanoes can make it cold but they can’t keep it cold.”

To account for the longevity issue, Miller and colleagues used computer modeling to determine how repeated short-lived episodes of volcanism might trigger a cooling period lasting several centuries. They found that the persistence of cold summers following the eruptions could be explained by a sea ice-ocean feedback originating in the North Atlantic Ocean.

Sustained cooling from repeated eruptions would have caused Arctic sea ice to expand southward until it eventually reached warmer waters and melted. Sea ice contains almost no salt, and when it melts it creates a less-dense freshwater cap over the salty seawater. This cap inhibits mixing and weakens heat transport from the tropics to the North Atlantic, creating a self-sustaining feedback system that could have lasted long after the effects of the volcanic aerosols subsided, Miller says.

Such a scenario is plausible, Schneider says. “This study is really the first to explain how a short-lived event like a volcanic eruption can trigger cooling that lasts for centuries.” However, there are still questions, he says. As of now, the weakest link in the study is the computer modeling, which depends on mere estimates of the size of the volcanic eruptions, Schneider says. There’s no accurate account of volcanic eruptions during this period.

The Little Ice Age is nominally stated to run from ~1250 AD to ~1850. That definition moves around a bit on the dates. Some make it start later (1550). However, the ending is generally agreed to be around the same time frame. The most common hypothesis is that the LIA was caused by the variation in solar activity (re Maunder Minimum, but not exclusively).

Monday, May 14, 2012

That’s right, the rumors appear to be true. Beijing is joining the
United States as the only nations with reusable spaceplane designs that
are actually conducting test flights. Beijing reportedly sent its Divine Dragon — or Shenlong — space plane aloft for a successful atmospheric
test flight in January, 2011. The U.S. uses its two X-37B spaceplanes for incredibly long missions
doing super classified work in place, one can only guess that China’s
Divine Dragon will be used for similar purposes.

Friday, May 04, 2012

New evidence proves humans are continuing to evolve and that
significant natural and sexual selection is still taking place in our
species in the modern world.

Despite advancements in medicine and technology, as well as an
increased prevalence of monogamy, research reveals humans are continuing
to evolve just like other species.

Scientists in an international collaboration, which includes the
University of Sheffield, analysed church records of about 6,000 Finnish
people born between 1760-1849 to determine whether the demographic,
cultural and technological changes of the agricultural revolution
affected natural and sexual selection in our species.

Project leader Dr Virpi Lummaa, of the University's Department of
Animal and Plant Sciences, said: "We have shown advances have not
challenged the fact that our species is still evolving, just like all
the other species 'in the wild'. It is a common misunderstanding that
evolution took place a long time ago, and that to understand ourselves
we must look back to the hunter-gatherer days of humans."

Dr Lummaa added: "We have shown significant selection has been
taking place in very recent populations, and likely still occurs, so
humans continue to be affected by both natural and sexual selection.
Although the specific pressures, the factors making some individuals
able to survive better, or have better success at finding partners and
produce more kids, have changed across time and differ in different
populations."

As for most animal species, the authors found that men and women are
not equal concerning Darwinian selection.

Principal investigator Dr Alexandre Courtiol, of the
Wissenschftskolleg zu Berlin, added: "Characteristics increasing the
mating success of men are likely to evolve faster than those increasing
the mating success of women. This is because mating with more partners
was shown to increase reproductive success more in men than in women.
Surprisingly, however, selection affected wealthy and poor people in the
society to the same extent."

The experts needed detailed information on large numbers of study
subjects to be able to study selection over the entire life cycle of
individuals: survival to adulthood, mate access, mating success, and
fertility per mate.

Thursday, May 03, 2012

Climate scientists at the Harvard School of Engineering and Applied Sciences (SEAS) have discovered that particulate pollution in the late 20th century created a "warming hole" over the eastern United States—that is, a cold patch where the effects of global warming were temporarily obscured.

While greenhouse gases like carbon dioxide and methane warm the Earth's surface, tiny particles in the air can have the reverse effect on regional scales.

"What we've shown is that particulate pollution over the eastern United States has delayed the warming that we would expect to see from increasing greenhouse gases," says lead author Eric Leibensperger (Ph.D. '11), who completed the work as a graduate student in applied physics at SEAS.

"For the sake of protecting human health and reducing acid rain, we've now cut the emissions that lead to particulate pollution," he adds, "but these cuts have caused the greenhouse warming in this region to ramp up to match the global trend."

At this point, most of the "catch-up" warming has already occurred.

The findings, published in the journal Atmospheric Chemistry and Physics, present a more complete picture of the processes that affect regional climate change. The work also carries significant implications for the future climate of industrial nations, like China, that have not yet implemented air quality regulations to the same extent as the United States.

Until the United States passed the Clean Air Act in 1970 and strengthened it in 1990, particulate pollution hung thick over the central and eastern states. Most of these particles in the atmosphere were made of sulfate, originating as sulfur emissions from coal-fired power plants. Compared to greenhouse gases, particulate pollution has a very short lifetime (about 1 week), so its distribution over the Earth is uneven.

"The primary driver of the warming hole is the aerosol pollution—these small particles," says Leibensperger. "What they do is reflect incoming sunlight, so we see a cooling effect at the surface."

This effect has been known for some time, but the new analysis demonstrates the strong impact that decreases in particulate pollution can have on regional climate.

The researchers found that interactions between clouds and particles amplified the cooling. Particles of pollution can act as nucleation sites for cloud droplets, which can in turn reflect even more sunlight than the particles would individually, leading to greater cooling at the surface.

This was something I brought up back in 2005 when I as working with the climate guys here. Pollution and particulates make a big difference.

That is just odd. No, no. I don't mean the awful animation in the beginning. I mean the bizarro video of what looks like civvies just walking around atop the plane. Anyone have any ideas on what is going on here?